1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a packaging structure of a driving circuit for a liquid crystal display device and a packaging method of the driving circuit for the liquid crystal display device.
2. Discussion of the Related Art
Flat panel display devices, that are thin, low weight and low power consumption, have been required as the information age rapidly evolves. The liquid crystal display device is widely used for notebook computers and desktop monitors, etc. because of its superior resolution, color image display and quality of displayed images.
Generally, the liquid crystal display device has upper and lower substrates, which are spaced apart and facing each other. Each of the substrate includes an electrode and the electrodes of each upper and lower substrate face each other. Liquid crystal is interposed between the upper substrate and the lower substrate. A voltage is applied to the liquid crystal through the electrodes of each substrate, and thus an alignment of the liquid crystal molecules is changed according the applied voltage to display images.
The liquid crystal display device mainly consists of a liquid crystal panel, which includes liquid crystal between the upper substrate and the lower substrate, a back light behind the liquid crystal panel and a driving unit in an outer side edge of the liquid crystal panel. The driving unit includes a driving circuit, i.e., a drive integrated circuit for applying signals to electric lines of the liquid crystal panel and the driving unit can be one of the following: a chip on glass (COG), a chip on film (COF) and a tape carrier package (TCP) depending on a packaging method of the drive integrated circuit to the liquid crystal panel. With a chip on glass (COG), the drive integrated circuit is packaged on an array substrate of the liquid crystal panel, a size of the liquid crystal panel increases. Whereas a compact structure can be obtained with a chip on film (COF) or the tape carrier package (TCP), because the drive integrated circuit is packaged using a film with the drive integrated circuit that can be bent toward a rear side of the liquid crystal panel. Accordingly, the chip on film (COF) or the tape carrier package (TCP) has been primarily used in the field. The chip on film (COF) or the tape carrier package (TCP) includes the film in which the drive integrated circuit is included.
FIG. 1 is a plan view illustrating a schematic structure of a typical liquid crystal display device that uses the chip on film (COF) or the tape carrier package (TCP). As shown in the figure, the liquid crystal panel 10 includes an array substrate 11 and a color filter substrate 12 and a liquid crystal layer (not shown) is interposed between the array substrate 11 and the color filter substrate 12. Because the array substrate 11 is larger than the color filter substrate 12, a portion of the array substrate 11 is not covered with the color filter substrate 12, and a pad (not shown) is formed on an outer, marginal space of the array substrate 11 to receive a signal to the electric line of the liquid crystal panel 10. The pad of the array substrate 11 is connected to the tape carrier package (TCP) (or the chip on film (COF)) 30 and the tape carrier package (TCP) (or the chip on film (COF)) 30 includes the drive integrated circuit 31 for driving the liquid crystal panel 10. The tape carrier package (TCP) (or the chip on film (COF)) 30 is also connected to a printed circuit board (PCB) 20. Alternatively, a back light (not shown) is positioned behind the liquid crystal panel 10 for a light source. The printed circuit board (PCB) is a board on which a plurality of elements such as an integrated circuit (IC) is formed and generates various control signals and data signals for driving the liquid crystal panel 10.
An anisotropic conductive film (ACF) is used for connecting the tape carrier package (TCP) (or the chip on film (COF)) 30 to the liquid crystal panel 10 or to the printed circuit board (PCB) 20. The anisotropic conductive film (ACF) is a type of a thermosetting resin containing a number of conductive particles. The connecting method for the liquid crystal panel 10 and the tape carrier package (TCP) (or the chip on film (COF)) 30 is as follows. First, the anisotropic conductive film (ACF) is pasted on the pad of the liquid crystal panel 10 and then the tape carrier package (TCP) (or the chip on film (COF)) 30 is attached to the anisotropic conductive film (ACF) on the pad of the liquid crystal panel 10. Finally, if the tape carrier package (TCP) is pressed to the anisotropic conductive film (ACF) using a heat, the tape carrier package (TCP) and the anisotropic conductive film (ACF) are electrically connected each other. Next, it is desirable to apply the proper heat and pressure suited for a material of the tape carrier package (TCP) and the anisotropic conductive film (ACF). The connecting method for the tape carrier package (TCP) (or the chip on film (COF)) 30 and the printed circuit board (PCB) 20 can be performed with the same process as that of the tape carrier package (TCP) 30 and the liquid crystal panel 10. Since the tape carrier package (TCP) and the chip on film (COF) use the film that is flexible, they are suitable for a compact structure. However, because a metal line thickness of the chip on film (COF) is thinner than a metal line thickness of the tape carrier package (TCP), the chip on film (COF) is suitable for patterning, and can have a finer structure than the tape carrier package (TCP).
A structure and a manufacturing process of the chip on film (COF) will be described hereinafter with reference to the figures. FIG. 2A and FIG. 2B being plan views illustrating a structure of a conventional chip on film (COF). FIG. 2A illustrates the chip on film (COF) of a gate driving circuit for applying a voltage to a gate signal line of the liquid crystal panel, and FIG. 2B illustrates the chip on film (COF) of a data driving circuit for applying a voltage to a data signal line of the liquid crystal panel. As shown in the figures, a plurality of input metal lines 60 and a plurality of output metal lines 70 are formed on a base film 50, maintaining a certain distance between them. An overcoat layer 80 is formed on the input metal lines 60 and the output metal lines 70. The overcoat layer 80 exposes terminals of the input metal lines 60 and the output metal lines 70; the drive integrated circuit 90 is connected to the terminals at one end of the input metal lines 60 and the output metal lines 70, respectively. Other terminals at the other end of the output metal lines 70 are connected to a gate pad (not shown) or a data pad (not shown) and other terminals at the other end of the input metal lines 60 are connected to the external printed circuit board (PCB). Each of the output metal lines 70 must correspond to each signal line of the liquid crystal panel. However, the number input metal lines 60 only have to be sufficient to deliver a signal generated in the printed circuit board (PCB) to the drive integrated circuit 90. Accordingly, fewer input metal lines 60 may be formed than the output metal lines 70 with a larger space between them than the output metal lines 70.
FIGS. 3A to 3C are plan views illustrating a packaging process of a chip on film (COF) of a data driving circuit according to the related art. In FIG. 3A, a plurality of input metal lines 60 and a plurality of output metal lines 70 are formed by patterning a metal film on a base film 50. Next, the input metal lines 60 and the output metal lines 70 are formed keeping a certain distance respectively between them. As described before, the input metal lines 60 can be formed with a larger interval space than the output metal lines 70.
In FIG. 3B, an overcoat layer 80, which exposes terminals of the input metal lines 60 and the output metal lines 70, is formed on the input metal lines 60 and the output metal lines 70, by patterning an insulating material on the input metal lines 60 and the output metal lines 70. The terminals at one end of the input metal lines 60 and the terminals adjacent thereto are exposed through an opening 81 of the overcoat layer 80.
In FIG. 3C, the exposed terminals of the input metal lines 60 and the output metal lines 70 are connected to a drive integrated circuit 90. The chip on film (COF) is attached to the liquid crystal panel and the printed circuit board (PCB) using an anisotropic conductive film (ACF) after the chip on film (COF) is manufactured according to the above processes.
FIG. 4 is a cross-sectional view taken along IV-IV of FIG. 3C. As shown in the figure, a pad pitch is defined as a summation of a terminal width “a” of the output metal lines 70 and a distance “d” between two output metal lines 70. An attainable minimum pad pitch of the chip on film (COF) is about 50 μm, considering a patterning accuracy for the metal film that is used for the metal lines, and prevention of an electric short during pasting the anisotropic conductive film (ACF). A liquid crystal display device has many pixels, one pixel consisting of three sub-pixels for red (R), green (G), and blue (B) colors. A pixel pitch is defined as a width of the sub-pixel. Because there is a space between two neighboring chip on films (COF), the pad pitch is smaller than the pixel pitch. With the demand for devices that have higher resolutions as the number of the pixels in a given area has increased while the pixel size is decreased. Accordingly, the pixel pitch and the pad pitch are being decreased. In case of a high-resolution liquid crystal display device, which has 200 to 300 pixels per inch (from 200 to 300 PPI), a maximum pixel pitch is 42 μm, and the pad pitch must be smaller than the maximum pixel pitch. Accordingly, a minimum pad pitch that can be achieved by now is 50 μm as described before, the chip on film (COF) (or the tape carrier package (TCP)) in FIG. 3C cannot be used for a high-resolution liquid crystal display device.
To overcome this problem, the pad pitch can be made greater than the pixel pitch by forming an area for packaging the chip on films (COF) larger than that of FIG. 1 as shown FIG. 5A. A double bank structure in which the chip on films (COF) are packaged in upper and lower sides of the liquid crystal panel may alternatively be used for the high-resolution liquid crystal display device as shown FIG. 5B. However, as the volume of the liquid crystal panel increases, the cost increases for the manufacturing process of a driving circuit and module.